1. Field of the Invention
The present invention relates to techniques for inspecting the quality of images printed on sheets.
2. Description of the Related Art
A digital printing technology of print on demand, which is based on an electrophotographic technology, has become widespread in the printing industry, and there is an increasing demand for producing print materials in a required amount efficiently while maintaining the print quality. Nowadays, there is also a need for producing print materials efficiently while maintaining the print quality in ordinary offices.
To date, the image quality of print materials has been inspected typically by an operator visually checking the print materials. Thus, the result is dependent on a sensory evaluation of the operator, and a variation in the inspection level may occur. In addition, the inspection time may vary depending on the skill level of the operator, and as the inspection relies on manpower, there is a limit on how much the inspection time can be shortened. Accordingly, an automatic inspection apparatus has been devised for inspecting the image quality of print materials.
Such an automatic inspection apparatus makes a determination by comparing inspection image data with reference data. The inspection image data corresponds to scan data obtained by reading a printed image by a sensor such as a scanner, and the reference data corresponds to document image data generated in a printing apparatus. The automatic inspection apparatus then determines the print quality of the print material based on whether the inspection image data matches the reference data.
Here, a case will be considered where, in the automatic inspection apparatus, a recording sheet on which printing is to be performed (hereinafter, referred to as a print material) is a recording sheet on which printing has already been performed in another image forming apparatus (hereinafter, referred to as a preprint sheet). Inspection image data obtained by scanning a print material that has been obtained by performing printing on a preprint sheet may be affected by content preprinted on the preprint sheet.
Thus, Japanese Patent Application Laid-Open No. 2006-238817 discusses a technique in which, after a print material that has been obtained by performing printing on a preprint sheet is scanned, inspection image data is generated while masking the preprint portion. This inspection image data is then compared with reference data, and thus the image quality can be inspected without being affected by the preprint printing.
Japanese Patent Application Laid-Open No. 2005-238817 also discusses a method in which inspection image data is generated while masking a preprint of scan data obtained by scanning a print material that has been obtained by performing printing on a preprint sheet. This inspection image data is then compared with reference data, and thus the image quality can be inspected without being affected by the preprint printing.
The assumption in Japanese Patent Application Laid-Open No. 2005-238817, however, is that a formatted document such as an invoice and a delivery note is used as a preprint sheet, and that a print area of document image data may overlap a printed area in a preprint sheet is not assumed.
If, for example, a preprint sheet on which printing has been lightly performed across the entire surface thereof is used, reference data in which the entire print area is masked is generated, leading to a problem that the image quality cannot be inspected.